Damper with digital valve

ABSTRACT

A shock absorber is disclosed having a pressure tube forming a working chamber, and a piston assembly slidably disposed within the pressure tube. The piston assembly may divide the working chamber into upper and lower working chambers. The piston assembly may have a piston body defining a first fluid passage extending therethrough and a first valve assembly controlling fluid flow through the first fluid passage. A second fluid passage, separate from the first fluid passage, extends from one of the upper and lower working chambers to a fluid chamber defined at least in part by the pressure tube. A plurality of digital valve assemblies are included and configured to exclusively control all fluid flow through the second fluid passage, and thus all fluid flow between the one of the upper and lower working chambers to the fluid chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/849,092, filed Sep. 9, 2015; which is a continuation of U.S. patentapplication Ser. No. 14/134,390 filed on Dec. 19, 2013 (now U.S. Pat.No. 9,150,077), which is a divisional of U.S. patent application Ser.No. 12/573,911 filed on Oct. 6, 2009 (now U.S. Pat. No. 8,616,351). Theentire disclosures of each of the above applications are incorporatedherein by reference.

FIELD

The present disclosure relates generally to hydraulic dampers or shockabsorbers for use in a suspension system such as a suspension systemused for automotive vehicles. More particularly, the present disclosurerelates to a digital damper valve which is combined with theconventional passive valve systems to determine the dampingcharacteristics of the hydraulic damper.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Shock absorbers are used in conjunction with automotive suspensionsystems to absorb unwanted vibrations which occur during driving. Toabsorb the unwanted vibrations, shock absorbers are generally connectedbetween the sprung portion (body) and the unsprung portion (suspension)of the automobile. A piston is located within a pressure tube of theshock absorber and the pressure tube is connected to the unsprungportion of the vehicle. The piston is connected to the sprung portion ofthe automobile through a piston rod which extends through the pressuretube. The piston divides the pressure tube into an upper working chamberand a lower working chamber both of which are filled with hydraulicfluid. Because the piston is able, through valving, to limit the flow ofthe hydraulic fluid between the upper and the lower working chamberswhen the shock absorber is compressed or extended, the shock absorber isable to produce a damping force which counteracts the vibration whichwould otherwise be transmitted from the unsprung portion to the sprungportion of the vehicle. In a dual-tube shock absorber, a fluid reservoiror reserve chamber is defined between the pressure tube and a reservetube. A base valve is located between the lower working chamber and thereserve chamber to also produce a damping force which counteracts thevibrations which would otherwise be transmitted from the unsprungportion of the vehicle to the sprung portion of the automobile.

As described above, for a dual-tube shock absorber, the valving on thepiston limits the flow of damping fluid between the upper and lowerworking chambers when the shock absorber is extended to produce adamping load. The valving on the base valve limits the flow of dampingfluid between the lower working chamber and the reserve chamber when theshock absorber is compressed to produce a damping load. For a mono-tubeshock absorber, the valving on the piston limits the flow of dampingfluid between the upper and lower working chambers when the shockabsorber is extended or compressed to produce a damping load. Duringdriving, the suspension system moves in jounce (compression) and rebound(extension). During jounce movements, the shock absorber is compressedcausing damping fluid to move through the base valve in a dual-tubeshock absorber or through the piston valve in a mono-tube shockabsorber. A damping valve located on the base valve or the pistoncontrols the flow of damping fluid and thus the damping force created.During rebound movements, the shock absorber is extended causing dampingfluid to move through the piston in both the dual-tube shock absorberand the mono-tube shock absorber. A damping valve located on the pistoncontrols the flow of damping fluid and thus the damping force created.

In a dual-tube shock absorber, the piston and the base valve normallyinclude a plurality of compression passages and a plurality of extensionpassages. During jounce or compression movements in a dual-tube shockabsorber, the damping valve or the base valve opens the compressionpassages in the base valve to control fluid flow and produce a dampingload. A check valve on the piston opens the compression passages in thepiston to replace damping fluid in the upper working chamber but thischeck valve does not contribute to the damping load. The damping valveon the piston closes the extension passages of the piston and a checkvalve on the base valve closes the extension passages of the base valveduring a compression movement. During rebound or extension movements ina dual-tube shock absorber, the damping valve on the piston opens theextension passages in the piston to control fluid flow and produce adamping load. A check valve on the base valve opens the extensionpassages in the base valve to replace damping fluid in the lower workingchamber but this check valve does not contribute to the damping load.

In a mono-tube shock absorber, the piston normally includes a pluralityof compression passages and a plurality of extension passages. The shockabsorber will also include means for compensating for the rod volumeflow of fluid as is well known in the art. During jounce or compressionmovements in a mono-tube shock absorber, the compression damping valveon the piston opens the compression passages in the piston to controlfluid flow and produce a damping load. The extension damping valve onthe piston closes the extension passages of the piston during a jouncemovement. During rebound or extension movements in a mono-tube shockabsorber, the extension damping valve on the piston opens the extensionpassages in the piston to control fluid flow and produce a damping load.The compression damping valve on the piston closes the compressionpassages of the piston during a rebound movement.

For most dampers, the damping valves are designed as a normal close/openvalve even though some valves may include a bleed flow of damping fluid.Because of this close/open design, these passive valve systems arelimited in their ability to adjust the generated damping load inresponse to various operating conditions of the vehicle.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one aspect the present disclosure relates to a shock absorber. Theshock absorber may comprise a pressure tube forming a working chamber,and a piston assembly slidably disposed within the pressure tube. Thepiston assembly may divide the working chamber into an upper workingchamber and a lower working chamber. The piston assembly may include apiston body defining a first fluid passage extending through the pistonbody and a first valve assembly controlling fluid flow through the firstfluid passage. A second fluid passage, separate from the first fluidpassage, extends from one of the upper and lower working chambers to afluid chamber defined at least in part by the pressure tube. A pluralityof digital valve assemblies are included and configured to exclusivelycontrol all fluid flow through the second fluid passage, and thus allfluid flow between the one of the upper and lower working chambers tothe fluid chamber. The fluid flow through the first valve assemblygenerates a high damping load for the shock absorber. Fluid flow throughthe first valve assembly and the digital valve assemblies cooperativelygenerate a low damping load, lower than the high damping load. Each ofthe plurality of digital valve assemblies may also include a firstmember, a second member disposed within the first member to move in anaxial direction within the first member, and a third member configuredto move the second member in the axial direction. The second member andthe first member of each one of the digital valve assemblies cooperateto exclusively control the fluid flow through the second fluid passagein the axial direction. Each of the digital valve assemblies may furtherinclude a single inlet and a first outlet, and fluid flow from thesingle inlet to the first outlet is in a first direction substantiallyparallel to the axial direction.

In another aspect the present disclosure provides a shock absorbercomprising a pressure tube forming a working chamber. A piston assemblymay be slidably disposed within the pressure tube. The piston assemblymay divide the working chamber into an upper working chamber and a lowerworking chamber. The piston assembly may include a piston body defininga first fluid passage extending through the piston body and a firstvalve assembly controlling fluid flow through the first fluid passage. Asecond fluid passage may be included which is separate from the firstfluid passage. The second fluid passage may extend from one of the upperand lower working chambers to a fluid chamber defined at least in partby the pressure tube. At least one digital valve assembly may beincluded for exclusively controlling all fluid flow through the secondfluid passage, and thus all fluid flow flowing between the one of theupper and lower working chambers and the fluid chamber. The fluid flowthrough the first valve assembly generates a high damping load for theshock absorber. Fluid flow through the first valve assembly and the atleast one digital valve assembly generate a low damping load, lower thanthe high damping load, for the shock absorber. The digital valveassembly may include a first member, a second member disposed within thefirst member to move in an axial direction within the first member, anda third member configured to move the second member in the axialdirection. The second member and the first member cooperate to controlfluid flow in the axial direction through the digital valve assembly.The digital valve assembly includes an annular inlet chamber and anoutlet chamber. Fluid flow from the annular inlet chamber to the outletchamber is turned 90 degrees from a radial flow to a flow having adirection substantially parallel to the axial direction, by said digitalvalve assembly.

In still another aspect the present disclosure relates to a shockabsorber. The shock absorber may comprise a pressure tube forming aworking chamber and a piston assembly slidably disposed within thepressure tube. The piston assembly may divide the working chamber intoan upper working chamber and a lower working chamber. The pistonassembly may include a piston body defining a first fluid passageextending through the piston body and a first valve assembly controllingfluid flow through the first fluid passage. A second fluid passage maybe included which is separate from the first fluid passage. The secondfluid passage may extend from one of the upper and lower workingchambers to a fluid chamber defined in part by the pressure tube. Aplurality of digital valve assemblies may be included for exclusivelycontrolling all fluid flow through the second fluid passage, and thusall fluid flow from the one of the upper and lower working chambers tothe fluid chamber. Fluid flow through the first valve assembly generatesa high damping load for the shock absorber. Fluid flow through the firstvalve assembly and the digital valve assemblies generates a low dampingload, lower than the high damping load, for the shock absorber. Each ofthe plurality of digital valve assemblies includes a first member, asecond member disposed within the first member to move in an axialdirection within the first member, and a third member configured to movethe second member in the axial direction. The second member and thefirst member cooperate to control fluid flow in the axial directionthrough each of the digital valve assemblies. Each of the digital valveassemblies may further include an annular chamber surrounding the secondmember. Fluid flow through each digital valve assembly is in a directionsubstantially parallel to the axial direction.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is an illustration of an automobile having shock absorbers whichincorporate the valve design in accordance with the present disclosure;

FIG. 2 is a side view, partially in cross-section of a dual-tube shockabsorber from FIG. 1 which incorporates the valve design in accordancewith the present disclosure;

FIG. 3 is an enlarged side view, partially in cross-section, of thepiston assembly from the shock absorber illustrated in FIG. 2;

FIG. 4 is an enlarged side view, partially in cross-section of the basevalve assembly from the shock absorber illustrated in FIG. 2;

FIG. 5 is an enlarged side view, partially in cross-section of thedigital valve assembly from the shock absorber illustrated in FIG. 2;

FIG. 6 is an enlarged cross-sectional perspective view of the digitalvalve assembly illustrated in FIGS. 2 and 5;

FIG. 7 is a graph of force vs. velocity for the shock absorberillustrated in FIGS. 2-6;

FIG. 8 is a side view, partially in cross-section, of a mono-tube shockabsorber which incorporates the valve design in accordance with thepresent disclosure;

FIG. 9 is an enlarged side view, partially in cross-section of thepiston assembly shown in FIG. 8;

FIG. 10 is an enlarged cross-sectional perspective view of the digitalvalve assembly illustrated in FIGS. 8 and 9;

FIG. 11 is an enlarged cross-sectional view of a shock absorber and rodguide assembly in accordance with another embodiment of the presentdisclosure;

FIG. 12 is an enlarged cross-sectional view of the digital valveassembly illustrated in FIG. 11;

FIG. 13 is an enlarged cross-sectional view of a piston rod assembly inaccordance with another embodiment of the present disclosure;

FIG. 14 is an enlarged cross-sectional view of the digital valveassembly illustrated in FIG. 13;

FIG. 15 is a cross-sectional side view of a shock absorber assembly inaccordance with another embodiment of the present disclosure;

FIG. 16 is an enlarged cross-sectional view of the digital valveassemblies illustrated in FIG. 15;

FIG. 17 is an enlarged cross-sectional perspective view of the basevalve assembly illustrated in FIGS. 15 and 16;

FIG. 18 is a cross-sectional view of a base valve assembly in accordancewith another embodiment of the present disclosure;

FIG. 19 is an enlarged cross-sectional perspective view of the basevalve assembly illustrated in FIG. 18;

FIG. 20 is a cross-sectional view of a base valve assembly in accordancewith another embodiment of the present disclosure; and

FIG. 21 is an enlarged cross-sectional perspective view of the basevalve assembly illustrated in FIG. 20.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. There isshown in FIG. 1 a vehicle incorporating a suspension system having shockabsorbers, each of which incorporates a valve assembly in accordancewith the present invention, and which is designated generally by thereference numeral 10. Vehicle 10 includes a rear suspension 12, a frontsuspension 14 and a body 16. Rear suspension 12 has a transverselyextending rear axle assembly (not shown) adapted to operatively supporta pair of rear wheels 18. The rear axle is attached to body 16 by meansof a pair of shock absorbers 20 and by a pair of springs 22. Similarly,front suspension 14 includes a transversely extending front axleassembly (not shown) to operatively support a pair of front wheels 24.The front axle assembly is attached to body 16 by means of a pair ofshock absorbers 26 and by a pair of springs 28. Shock absorbers 20 and26 serve to dampen the relative motion of the unsprung portion (i.e.,front and rear suspensions 12, 14) with respect to the sprung portion(i.e., body 16) of vehicle 10. While vehicle 10 has been depicted as apassenger car having front and rear axle assemblies, shock absorbers 20and 26 may be used with other types of vehicles or in other types ofapplications including, but not limited to, vehicles incorporatingnon-independent front and/or non-independent rear suspensions, vehiclesincorporating independent front and/or independent rear suspensions orother suspension systems known in the art. Further, the term “shockabsorber” as used herein is meant to refer to dampers in general andthus will include McPherson struts and other damper designs known in theart.

Referring now to FIG. 2, shock absorber 20 is shown in greater detail.While FIG. 2 illustrates only shock absorber 20, it is to be understoodthat shock absorber 26 also includes the valve assembly design describedbelow for shock absorber 20. Shock absorber 26 only differs from shockabsorber 20 in the manner in which it is adapted to be connected to thesprung and unsprung masses of vehicle 10. Shock absorber 20 comprises apressure tube 30, a piston assembly 32, a piston rod 34, a reserve tube36 and a base valve assembly 38.

Pressure tube 30 defines a working chamber 42. Piston assembly 32 isslidably disposed within pressure tube 30 and divides working chamber 42into an upper working chamber 44 and a lower working chamber 46. A seal48 is disposed between piston assembly 32 and pressure tube 30 to permitsliding movement of piston assembly 32 with respect to pressure tube 30without generating undue frictional forces as well as sealing upperworking chamber 44 from lower working chamber 46. Piston rod 34 isattached to piston assembly 32 and extends through upper working chamber44 and through a rod guide assembly 50 which closes the upper end ofpressure tube 30. The end of piston rod 34 opposite to piston assembly32 is adapted to be secured to the sprung mass of vehicle 10. Valvingwithin piston assembly 32 controls the movement of fluid between upperworking chamber 44 and lower working chamber 46 during movement ofpiston assembly 32 within pressure tube 30. Because piston rod 34extends only through upper working chamber 44 and not lower workingchamber 46, movement of piston assembly 32 with respect to pressure tube30 causes a difference in the amount of fluid displaced in upper workingchamber 44 and the amount of fluid displaced in lower working chamber46. The difference in the amount of fluid displaced is known as the “rodvolume” and it flows through base valve assembly 38.

Reserve tube 36 surrounds pressure tube 30 to define a fluid reservoirchamber 52 located between tubes 30 and 36. The bottom end of reservetube 36 is closed by a base cup 54 which is adapted to be connected tothe unsprung mass of vehicle 10. The upper end of reserve tube 36 isattached to rod guide assembly 50. Base valve assembly 38 is disposedbetween lower working chamber 46 and reservoir chamber 52 to control theflow of fluid between chambers 46 and 52. When shock absorber 20 extendsin length, an additional volume of fluid is needed in lower workingchamber 46 due to the “rod volume” concept. Thus, fluid will flow fromreservoir chamber 52 to lower working chamber 46 through base valveassembly 38 as detailed below. When shock absorber 20 compresses inlength, an excess of fluid must be removed from lower working chamber 46due to the “rod volume” concept. Thus, fluid will flow from lowerworking chamber 46 to reservoir chamber 52 through base valve assembly38 as detailed below.

Referring now to FIG. 3, piston assembly 32 comprises a piston body 60,a compression valve assembly 62 and a rebound valve assembly 64.Compression valve assembly 62 is assembled against a shoulder 66 onpiston rod 34. Piston body 60 is assembled against compression valveassembly 62 and rebound valve assembly 64 is assembled against pistonbody 60. A nut 68 secures these components to piston rod 34.

Piston body 60 defines a plurality of compression passages 70 and aplurality of rebound passages 72. Seal 48 includes a plurality of ribs74 which mate with a plurality of annular grooves 76 to retain seal 48during sliding movement of piston assembly 32.

Compression valve assembly 62 comprises a retainer 78, a valve disc 80and a spring 82. Retainer 78 abuts shoulder 66 on one end and pistonbody 60 on the other end. Valve disc 80 abuts piston body 60 and closescompression passages 70 while leaving rebound passages 72 open. Spring82 is disposed between retainer 78 and valve disc 80 to bias valve disc80 against piston body 60. During a compression stroke, fluid in lowerworking chamber 46 is pressurized causing fluid pressure to reactagainst valve disc 80. When the fluid pressure against valve disc 80overcomes the biasing load of spring 82, valve disc 80 separates frompiston body 60 to open compression passages 70 and allow fluid flow fromlower working chamber 46 to upper working chamber 44. Typically spring82 only exerts a light load on valve disc 80 and compression valveassembly 62 acts as a check valve between chambers 46 and 44. Thedamping characteristics for shock absorber 20 during a compressionstroke are controlled in part by base valve assembly 38 whichaccommodates the flow of fluid from lower working chamber 46 toreservoir chamber 52 due to the “rod volume” concept. During a reboundstroke, compression passages 70 are closed by valve disc 80.

Rebound valve assembly 64 is termed a passive valve assembly whichcomprises a spacer 84, a plurality of valve discs 86, a retainer 88 anda spring 90. Spacer 84 is threadingly received on piston rod 34 and isdisposed between piston body 60 and nut 68. Spacer 84 retains pistonbody 60 and compression valve assembly 62 while permitting thetightening of nut 68 without compressing either valve disc 80 or valvediscs 86. Retainer 78, piston body 60 and spacer 84 provide a continuoussolid connection between shoulder 66 and nut 68 to facilitate thetightening and securing of nut 68 to spacer 84 and thus to piston rod34. Valve discs 86 are slidingly received on spacer 84 and abut pistonbody 60 to close rebound passages 72 while leaving compression passages70 open. Retainer 88 is also slidingly received on spacer 84 and itabuts valve discs 86. Spring 90 is assembled over spacer 84 and isdisposed between retainer 88 and nut 68 which is threadingly received onspacer 84. Spring 90 biases retainer 88 against valve discs 86 and valvediscs 86 against piston body 60. When fluid pressure is applied to valvediscs 86, they will elastically deflect at the outer peripheral edge toopen rebound valve assembly 64. A shim is located between nut 68 andspring 90 to control the preload for spring 90 and thus the blow offpressure as described below. Thus, the calibration for the blow offfeature of rebound valve assembly 64 is separate from the calibrationfor compression valve assembly 62.

During a rebound stroke, fluid in upper working chamber 44 ispressurized causing fluid pressure to react against valve discs 86.Prior to the deflecting of valve discs 86, a bleed flow of fluid flowsthrough a bleed passage defined between valve discs 86 and piston body60. When the fluid pressure reacting against valve discs 86 overcomesthe bending load for valve discs 86, valve discs 86 elastically deflectopening rebound passages 72 allowing fluid flow from upper workingchamber 44 to lower working chamber 46. The strength of valve discs 86and the size of rebound passages will determine the dampingcharacteristics for shock absorber 20 in rebound. When the fluidpressure within upper working chamber 44 reaches a predetermined level,the fluid pressure will overcome the biasing load of spring 90 causingaxial movement of retainer 88 and the plurality of valve discs 86. Theaxial movement of retainer 88 and valve discs 86 fully opens reboundpassages 72 thus allowing the passage of a significant amount of dampingfluid creating a blowing off of the fluid pressure which is required toprevent damage to shock absorber 20 and/or vehicle 10.

Referring to FIG. 4, base valve assembly 38 comprises a valve body 92, acompression valve assembly 94 and a rebound valve assembly 96.Compression valve assembly 94 and rebound valve assembly 96 are attachedto valve body 92 using a bolt 98 and a nut 100. The tightening of nut100 biases compression valve assembly 94 towards valve body 92. Valvebody 92 defines a plurality of compression passages 102 and a pluralityof rebound passages 104.

Compression valve assembly 94 is termed a passive valve assembly whichcomprises a plurality of valve discs 106 that are biased against valvebody 92 by bolt 98 and nut 100. During a compression stroke, fluid inlower working chamber 46 is pressurized and the fluid pressure withincompression passages 102 reacts against valve discs 106. Prior to thedeflection of valve discs 106, a bleed flow of fluid will flow through ableed passage defined between valve discs 106 and valve body 92. Thefluid pressure reacting against valve discs 106 will eventually opencompression valve assembly 94 by deflecting valve discs 106 in a mannersimilar to that described above for rebound valve assembly 64.Compression valve assembly 62 will allow fluid flow from lower workingchamber 46 to upper working chamber 44 and only the “rod volume” willflow through compression valve assembly 94. The damping characteristicsfor shock absorber 20 are determined in part by the design ofcompression valve assembly 94 of base valve assembly 38.

Rebound valve assembly 96 comprises a valve disc 108 and a valve spring110. Valve disc 108 abuts valve body 92 and closes rebound passages 104.Valve spring 110 is disposed between nut 100 and valve disc 80 to biasvalve disc 108 against valve body 92. During a rebound stroke, fluid inlower working chamber 46 is reduced in pressure causing fluid pressurein reservoir chamber 52 to react against valve disc 108. When the fluidpressure against valve disc 108 overcomes the biasing load of valvespring 110, valve disc 108 separates from valve body 92 to open reboundpassages 104 and allow fluid flow from reservoir chamber 52 to lowerworking chamber 46. Typically valve spring 110 exerts only a light loadon valve disc 108 and compression valve assembly 94 acts as a checkvalve between reservoir chamber 52 and lower working chamber 46. Thedamping characteristics for a rebound stroke are controlled in part byrebound valve assembly 64 as detailed above.

Referring now to FIGS. 5 and 6, rod guide assembly 50 is illustrated ingreater detail. Rod guide assembly 50 comprises a rod guide housing 120,a seal assembly 122, a retainer 124 and a digital valve assembly 126.

Rod guide housing 120 is assembled into pressure tube 30 and intoreserve tube 36. Seal assembly 122 and retainer 124 are assembled to rodguide housing 120 and reserve tube 36 is rolled or formed over asillustrated at 128 to retain rod guide assembly 50. A bushing 130assembled into rod guide housing 120 accommodates for the sliding motionof piston rod 34 while also providing for a seal for piston rod 34. Afluid passage 132 extends through rod guide housing 120 to allow fluidcommunication between upper working chamber 44 and digital valveassembly 126 as discussed below.

Digital valve assembly 126 is a two position valve assembly which has adifferent flow area in each of the two positions. Digital valve assembly126 comprises a valve housing 140, a sleeve 142, a spool 144, a spring146 and a coil assembly 148. Valve housing 140 defines a valve inlet 150which is in communication with upper working chamber 44 through fluidpassage 132 and a valve outlet 152 which is in fluid communication withreservoir chamber 52. While this embodiment and other embodimentsdescribed later include spring 146 in the digital valve assemblies, itis within the scope of the present disclosure to use digital valveassemblies that do not include spring 146. Digital valve assemblies thatdo not include spring 146 are moved between their two positions byreversing the current or reversing the polarity of the power provided tothe digital valve assembly.

Sleeve 142 is disposed within valve housing 140. Sleeve 142 defines anannular inlet chamber 154 which is in communication with valve inlet 150and a pair of annular outlet chambers 156 and 158 which are incommunication with valve outlet 152.

Spool 144 is slidingly received within sleeve 142 and axially travelswithin sleeve 142 between coil assembly 148 and a stop puck 160 disposedwithin sleeve 142. Spring 146 biases spool 144 away from coil assembly148 and towards stop puck 160. A shim 162 is disposed between coilassembly 148 and sleeve 142 to control the amount of axial motion forspool 144. A first O-ring seals the interface between stop puck 160,sleeve 142 and valve housing 140. A second O-ring seals the interfacebetween coil assembly 148, sleeve 142 and rod guide housing 120.

Spool 144 defines a first flange 164 which controls fluid flow betweenannular inlet chamber 154 and annular outlet chamber 156 and a secondflange 166 that controls fluid flow between annular inlet chamber 154and annular outlet chamber 158. Flanges 164 and 166 thus control fluidflow from upper working chamber 44 to reservoir chamber 52.

Coil assembly 148 is disposed within sleeve 142 to control the axialmovement of spool 144. The wiring connections for coil assembly 148 canextend through rod guide housing 120, through sleeve 142, through valvehousing 140 and/or through reserve tube 36. When there is no powerprovided to coil assembly 148, the damping characteristics will bedefined by the flow area of digital valve assembly 126 in its firstposition, piston assembly 32 and base valve assembly 38. The movement ofspool 144 is controlled by supplying power to coil assembly 148 to movedigital valve assembly to its second position. Digital valve assembly126 can be kept in its second position by continuing to supply power tocoil assembly 148 or by providing means for retaining digital valveassembly 126 in its second position and discontinuing the supply ofpower to coil assembly 148. The means for retaining digital valveassembly 126 in its second position can include mechanical means,magnetic means or other means known in the art. Once in its secondposition, movement to the first position can be accomplished byterminating power to coil assembly 148 or by reversing the current orreversing the polarity of the power supplied to coil assembly 148 toovercome the retaining means. The amount of flow through digital valveassembly 126 has discrete settings for flow control in both the firstposition and the second position. While the present disclosure isdescribed using only one digital valve assembly 126, it is within thescope of the disclosure to use a plurality of digital valve assemblies126. When multiple digital valve assemblies 126 are used, the total flowarea through the plurality of digital valve assemblies 126 can be set ata specific number of total flow areas depending on the position of eachindividual digital valve assemblies 126. The specific number of totalflow areas can be defined as being 2^(n) flow areas where n is thenumber of digital valve assemblies 126. For example, if four digitalvalve assemblies 126, the number of total flow areas available would be2⁴ or sixteen flow areas.

FIG. 7 discloses a force vs. velocity curve for shock absorber 20. LineA represents the bleed flow and the firm setting when digital valveassembly 126 is closed. Line B represents the bleed flow and thecombination of the passive valving in piston assembly 32 or base valveassembly 38 in combination with a first opening degree of digital valveassembly 126. Line C represents the bleed flow and the combination ofthe passive valving in piston assembly 32 or base valve assembly 38 incombination with a second opening degree of digital valve assembly 126greater than the first opening degree. Line D represents the bleed flowand the combination of the passive valving in piston assembly 32 or basevalve assembly 38 in combination with a fully opened digital valveassembly 126.

Fluid will flow through digital valve assembly 126 will occur bothduring a rebound or extension stroke and during a compression stroke.During a rebound or extension stroke, fluid in upper working chamber 44is pressurized which then forces fluid flow through digital valveassembly 126 when it is opened. During a compression stroke, fluid flowsfrom lower working chamber 46 to upper working chamber 44 through pistonassembly 32 due to the “rod volume” concept. When digital valve assembly126 is opened, an open flow path between upper working chamber 44 andreservoir chamber 52 is created. Additional fluid flow will flow throughpiston assembly 32 and through digital valve assembly 126 because thisopen flow path creates the path of least resistance to reservoir chamber52 in comparison to flow through base valve assembly 38.

Referring now to FIG. 8-10, a mono-tube shock absorber 220 in accordancewith the present invention is illustrated. Shock absorber 220 canreplace either shock absorber 20 or shock absorber 26 by modifying theway it is adapted to be connected to the sprung mass and/or the unsprungmass of the vehicle. Shock absorber 220 comprises a pressure tube 230, apiston assembly 232 and a piston rod assembly 234.

Pressure tube 230 defines a working chamber 242. Piston assembly 232 isslidably disposed within pressure tube 230 and divides working chamber242 into an upper working chamber 244 and a lower working chamber 246. Aseal 248 is disposed between piston assembly 232 and pressure tube 230to permit sliding movement of piston assembly 232 with respect topressure tube 230 without generating undue frictional forces as well assealing upper working chamber 244 from lower working chamber 246. Pistonrod assembly 234 is attached to piston assembly 232 and it extendsthrough upper working chamber 244 and through an upper end cap or rodguide 250 which closes the upper end of pressure tube 230. A sealingsystem seals the interface between rod guide 250, pressure tube 230 andpiston rod assembly 234. The end of piston rod assembly 234 opposite topiston assembly 232 is adapted to be secured to the sprung mass ofvehicle 10. The end of pressure tube 230 opposite to rod guide 250 isclosed by a base cup 254 which is adapted to be connected to theunsprung mass of vehicle 10.

A compression valve assembly 256 associated with piston assembly 232 istermed a passive valve assembly which controls movement of fluid betweenlower working chamber 246 and upper working chamber 244 duringcompression movement of piston assembly 232 within pressure tube 230.The design for compression valve assembly 256 controls in part thedamping characteristics for shock absorber 220 during a compressionstroke. An extension valve assembly 258 associated with piston assembly232 is termed a pressure valve assembly which controls movement of fluidbetween upper working chamber 244 and lower working chamber 246 duringextension or rebound movement of piston assembly 232 within pressuretube 230. The design for extension valve assembly 258 controls in partthe damping characteristics for shock absorber 220 during an extensionor rebound stroke.

Because piston rod assembly 234 extends only through upper workingchamber 244 and not lower working chamber 246, movement of pistonassembly 232 with respect to pressure tube 230 causes a difference inthe amount of fluid displaced in upper working chamber 244 and theamount of fluid displaced in lower working chamber 246. The differencein the amount of fluid displaced is known as the “rod volume” andcompensation for this fluid is accommodated by a piston slidablydisposed within pressure tube 230 and located between lower workingchamber 246 and a compensation chamber 260. Typically compensationchamber 260 is filled with a pressurized gas and the piston moves withinpressure tube 230 to compensate for the “rod volume” concept.

Referring now to FIG. 9, piston assembly 232 comprises a piston body262, compression valve assembly 256 and extension valve assembly 258.Compression valve assembly 256 is assembled against a shoulder 266 onpiston rod assembly 234. Piston body 262 is assembled againstcompression valve assembly 256 and extension valve assembly 258 isassembled against piston body 262. A nut 268 secures these components topiston rod assembly 234.

Piston body 262 defines a plurality of compression passages 270 and aplurality of rebound passages 272. Seal 248 includes a plurality of ribs274 which mate with a plurality of annular grooves 276 to retain seal248 during sliding movement of piston assembly 232.

Compression valve assembly 256 is termed a passive valve assembly whichcomprises a retainer 278, a valve disc 280 and a spring 282. Retainer278 abuts shoulder 266 on one end and piston body 262 on the other end.Valve disc 280 abuts piston body 262 and closes compression passages 270while leaving rebound passages 272 open. Spring 282 is disposed betweenretainer 278 and valve disc 280 to bias valve disc 280 against pistonbody 262. During a compression stroke, fluid in lower working chamber246 is pressurized causing fluid pressure to react against valve disc280. Prior to the opening of valve disc 280, a bleed flow of fluid willflow through a bleed passage defined by valve disc 280 and piston body262. When the fluid pressure against valve disc 280 overcomes thebiasing load of spring 282, valve disc 280 separates from piston body262 to open compression passages 270 and allow fluid flow from lowerworking chamber 246 to upper working chamber 244. The dampingcharacteristics for shock absorber 220 during a compression stroke arecontrolled by compression valve assembly 256. During a rebound stroke,compression passages 270 are closed by valve disc 280.

Extension valve assembly 258 is termed a passive valve assembly whichcomprises a spacer 284, a plurality of valve discs 286, a retainer 288and a spring 290. Spacer 284 is threadingly received on piston rodassembly 234 and is disposed between piston body 262 and nut 268. Spacer284 retains piston body 262 and compression valve assembly 256 whilepermitting the tightening of nut 268 without compressing either valvedisc 280 or valve discs 286. Retainer 278, piston body 262 and spacer284 provide a continuous solid connection between shoulder 266 and nut268 to facilitate the tightening and securing of nut 268 to spacer 284and thus to piston rod assembly 234. Valve discs 286 are slidinglyreceived on spacer 284 and abut piston body 262 to close reboundpassages 272 while leaving compression passages 270 open. Retainer 288is also slidingly received on spacer 284 and it abuts valve discs 286.Spring 290 is assembled over spacer 284 and is disposed between retainer288 and nut 268 which is threadingly received on spacer 284. Spring 290biases retainer 288 against valve discs 286 and valve discs 286 againstpiston body 262. When fluid pressure is applied to valve discs 286, theywill elastically deflect at the outer peripheral edge to open extensionvalve assembly 258. A shim 296 is located between nut 268 and spring 290to control the preload for spring 290 and thus the blow off pressure asdescribed below. Thus, the calibration for the blow off feature ofextension valve assembly 258 is separate from the calibration forcompression valve assembly 256.

During a rebound stroke, fluid in upper working chamber 244 ispressurized causing fluid pressure to react against valve discs 286.Prior to the deflection of valve discs 286, a bleed flow of fluid willflow through a bleed passage defined by valve discs 286 and piston body262. When the fluid pressure reacting against valve discs 286 overcomesthe bending load for valve discs 286, valve discs 286 elasticallydeflect opening rebound passages 272 allowing fluid flow from upperworking chamber 244 to lower working chamber 246. The strength of valvediscs 286 and the size of rebound passages will determine the dampingcharacteristics for shock absorber 220 in rebound. When the fluidpressure within upper working chamber 244 reaches a predetermined level,the fluid pressure will overcome the biasing load of spring 290 causingaxial movement of retainer 288 and the plurality of valve discs 286. Theaxial movement of retainer 288 and valve discs 286 fully opens reboundpassages 272 thus allowing the passage of a significant amount ofdamping fluid creating a blowing off of the fluid pressure which isrequired to prevent damage to shock absorber 220 and/or vehicle 10.

Referring now to FIG. 10, piston rod assembly 234 is illustrated ingreater detail. Piston rod assembly 234 comprises a piston rod 298 and adigital valve assembly 300. Piston rod 298 is a hollow piston rod thatdefines an internal bore 302 within which digital valve assembly 300 islocated. An inlet passage 304 extends through the lower post portion ofpiston rod 298 to allow communication between lower working chamber 246and internal bore 302. One or more outlet passages 306 extend throughpiston rod 298 to allow communication between upper working chamber 244and internal bore 302.

Digital valve assembly 300 is a two position valve assembly which has adifferent flow area in each of the two positions. Digital valve assembly300 comprises a sleeve 312, a plurality of spools 144, a plurality ofsprings 146, a plurality of coil assemblies 148 and a circuit board 314.Sleeve 312 defines a valve inlet 320 which is in communication withlower working chamber 246 through inlet passage 304; a valve outlet 322which is in communication with upper working chamber 244 through outletpassages 306; a plurality of annular inlet chambers 324 each of which isin communication valve inlet 320; and a pair of annular outlet chamber326, 328 associated with each inlet chamber 324 and each of which is incommunication with valve outlet 322.

Each spool 144 is slidingly received within sleeve 312 and axiallytravels within sleeve 312 between a respective coil assembly 148 and arespective stop puck 160 disposed within sleeve 312. Each spring 146biases a respective spool 144 away from coil assembly 148 and towardsstop puck 160. A respective shim 162 is disposed between each coilassembly 148 and each spool 144 to control the amount of axial motionfor spool 144. A first O-ring seals the interface between stop puck 160,sleeve 142 and piston rod 298. A second O-ring seals the interfacebetween coil assembly 148, sleeve 142 and circuit board 314.

Spool 144 defines first flange 164 which controls fluid flow between arespective annular inlet chamber 324 and a respective annular outletchamber 326 and second flange 166 that controls fluid flow between therespective annular inlet chamber 324 and a respective annular outletchamber 328. Flanges 164 and 166 thus control fluid flow between upperworking chamber 244 and lower working chamber 246.

Each coil assembly 148 is disposed within sleeve 312 to control theaxial movement of a respective spool 144. The wiring connections forcoil assemblies 148 extend to circuit board 314 and then throughinternal bore 302 of piston rod 298. Circuit board 314 is disposed ininternal bore 302 immediately above sleeve 312. An O-ring seals theinterface between circuit board 314 and piston rod 298. While circuitboard 314 is illustrated as being in internal bore 302, it is within thescope of the present disclosure to locate circuit board 314 external toshock absorber 220. When there is no power provided to coil assemblies148, the damping characteristics will be defined by the flow area ofeach digital valve assembly 300 in its first position and pistonassembly 232. The movement of each spool 144 is controlled by supplyingpower provided to each coil assembly 148 to move the respective digitalvalve assembly to its second position. Digital valve assemblies 300 canbe kept in the second position by continuing to supply power to eachcoil assembly 148 or by providing means for retaining digital valveassemblies 300 in the second position and discontinuing the supply ofpower to each coil assembly 148. The means for retaining each digitalvalve assembly 300 in its second position can include mechanical means,magnetic means or other means known in the art. Once in its secondposition, movement to the first position can be accomplished byterminating power to each coil assembly 148 or by reversing the currentor reversing the polarity of the power supplied to each coil assembly148 to overcome the retaining means. The amount of flow through eachdigital valve assembly 300 has discrete settings for flow control inboth the first position and the second position. While the presentdisclosure is described using multiple digital valve assemblies 300, itis within the scope of the disclosure to use one digital valve assembly300. When multiple digital valve assemblies 300 are used, the total flowarea through the plurality of digital valve assemblies 300 can be set ata specific number of total flow areas depending on the position of eachindividual digital valve assemblies 300. The specific number of totalflow areas can be defined as being 2^(n) flow areas where n is thenumber of digital valve assemblies 300. For example, if four digitalvalve assemblies 300, the number of total flow areas available would be2⁴ or sixteen flow areas.

The force vs. velocity curve for shock absorber 20 illustrated in FIG. 7is applicable to shock absorber 220. The curves A, B, C and Dillustrated in FIG. 7 are achieved using digital valve assembly 300.

Referring now to FIGS. 11-12, a rod guide assembly 400 in accordancewith the present disclosure is illustrated. Rod guide assembly 400 canbe used in place of rod guide assembly 50. Rod guide assembly 400comprises a rod guide housing 420, a seal assembly 422, and a pluralityof digital valve assemblies 426.

Rod guide housing 420 is assembled into pressure tube 30 and intoreserve tube 36. Seal assembly 422 is assembled to rod guide housing 420and reserve tube 36 is rolled or formed over as illustrated at 428 toretain rod guide assembly 400. One or more bushings 430 assembled intorod guide housing 420 accommodates for the sliding motion of piston rod34 while also providing for a seal for piston rod 34. A fluid passage432 extends through rod guide housing 420 to allow fluid communicationbetween upper working chamber 44 and digital valve assembly 426 asdiscussed below. A fluid passage 434 extends through rod guide housing420 to allow fluid communication between digital valve assembly 426 andreservoir chamber 52. A plurality of seal ports 436 extend through rodguide housing 420 to accommodate the flow of fluid between piston rod 34and bushings 430.

Each digital valve assembly 426 is identical and thus only one digitalvalve assembly 426 will be described. It is to be understood that thedescription below applies to all digital valve assemblies used in rodguide assembly 400. Digital valve assembly 426 is a two position valveassembly which has a different flow area in each of the two positions.Digital valve assembly 426 comprises a sleeve 442, spool 144, spring 146and coil assembly 148. Sleeve 442 is disposed within a valve port 450defined by rod guide housing 420. Sleeve 442 defines an annular inletchamber 454 which is in communication with fluid passage 432 and a pairof annular outlet chambers 456 and 458 which are in communication withfluid passage 434.

Spool 144 is slidingly received within sleeve 442 and axially travelswithin sleeve 442 between coil assembly 148 and stop puck 160 disposedwithin sleeve 442. Spring 146 biases spool 144 away from coil assembly148 and towards stop puck 160. Shim 162 is disposed between coilassembly 148 and spool 144 to control the amount of axial motion forspool 144. A first O-ring seals the interface between stop puck 160 anda retainer 460 secured to sleeve 442. A second O-ring seals theinterface between coil assembly 148 and a retainer 462 secured to sleeve442.

Spool 144 defines first flange 164 which controls fluid flow betweenannular inlet chamber 454 and annular outlet chamber 456 and secondflange 166 that controls fluid flow between annular inlet chamber 454and annular outlet chamber 458. Flanges 164 and 166 thus control fluidflow from upper working chamber 44 to reservoir chamber 52.

Coil assembly 148 is disposed within sleeve 442 to control the axialmovement of spool 144. The wiring connections for coil assembly 148 canextend through rod guide housing 420, through sleeve 442 and/or throughreserve tube 36. When there is no power provided to coil assembly 148,the damping characteristics will be defined by the flow area of digitalvalve assembly 426 in its first position, piston assembly 32 and basevalve assembly 38. The movement of spool 144 is controlled by supplyingpower to coil assembly 148 to move digital valve assembly to its secondposition. Digital valve assembly 426 can be kept in its second positionby continuing to supply power to coil assembly 148 or by providing meansfor retaining digital valve assembly 426 in its second position anddiscontinuing the supply of power to coil assembly 148. The means forretaining digital valve assembly 426 in its second position can includemechanical means, magnetic means or other means known in the art. Oncein its second position, movement to the first position can beaccomplished by terminating power to coil assembly 148 or by reversingthe current or reversing the polarity of the power supplied to coilassembly 148 to overcome the retaining means. The amount of flow throughdigital valve assembly 426 has discrete settings for flow control inboth the first position and the second position. While the presentdisclosure is described using a plurality of digital valve assemblies426, it is within the scope of the disclosure to use a single digitalvalve assembly 426. Similar to rod guide assembly 50, digital valveassemblies 426 control damping loads in both extension and compressionstrokes for shock absorber 20. When multiple digital valve assemblies426 are used, the total flow area through the plurality of digital valveassemblies 426 can be set at a specific number of total flow areasdepending on the position of each individual digital valve assemblies426. The specific number of total flow areas can be defined as being2^(n) flow areas where n is the number of digital valve assemblies 426.For example, if four digital valve assemblies 426, the number of totalflow areas available would be 2⁴ or sixteen flow areas.

The force vs. velocity curve for shock absorber 20 illustrated in FIG. 7is applicable to shock absorber 20 when it incorporates rod guideassembly 400 in place of rod guide assembly 50. The curves A, B, C and Dillustrated in FIG. 7 are achieved using digital valve assemblies 426.

Seal assembly 422 includes a check seal 470 which allows fluid to flowfrom the interface between piston rod 34 and bushings 430 to reservoirchamber 52 through seal ports 436 and fluid passage 434 but prohibitfluid flow from reservoir chamber 52 or fluid passage 434 through sealports 436 to the interface between piston rod 34 and bushings 430. Theupper portion of sleeve 442, above retainer 462 defines a flow passage472 to allow fluid flow from seal ports 436 to reach fluid passage 434and thus reservoir chamber 52.

Referring now to FIGS. 13 and 14, a piston rod assembly 500 inaccordance with the present disclosure is illustrated. Piston rodassembly 500 can be used in place of piston rod assembly 234. Piston rodassembly 500 comprises a piston rod 508 and a plurality of digital valveassemblies 510. Piston rod 508 is a hollow piston rod that defines aninternal bore 512 within which the plurality of digital valve assemblies510 are located. An inlet passage 514 extends through the lower postportion of piston rod 508 to allow communication between lower workingchamber 246 and internal bore 512. One or more outlet passages 516extend through piston rod 508 to allow communication between upperworking chamber 244 and internal bore 512.

As illustrated in FIG. 13, the plurality of digital valve assemblies 510are stacked atop each other within internal bore 512. Each digital valveassembly 510 is identical and thus, only one digital valve assembly willbe described. It is to be understood that the description below appliesto all digital valve assemblies 510 used in piston rod assembly 500.

Digital valve assembly 510 is a two position valve assembly which has adifferent flow area in each of the two positions. Digital valve assembly510 comprises a sleeve 522, spool 144, spring 146 and coil assembly 148.A single circuit board 524 is utilized for the plurality of digitalvalve assemblies 510. Sleeve 522 defines a valve inlet 530 which is incommunication with lower working chamber 246 through inlet passage 514;a valve outlet 532 which is in communication with upper working chamber244 through outlet passages 516; an annular inlet chamber 534 each ofwhich is in communication valve inlet 530; and a pair of annular outletchamber 536, 538 associated with inlet chamber 534 and each of which isin communication with valve outlet 532.

Each spool 144 is slidingly received within sleeve 522 and axiallytravels within sleeve 522 between coil assembly 148 and stop puck 160disposed within sleeve 522. Spring 146 biases spool 144 away from coilassembly 148 and towards stop puck 160. Shim 162 is disposed betweencoil assembly 148 and sleeve 522 to control the amount of axial motionfor spool 144. A first O-ring seals the interface between stop puck 160and a washer 540 attached to sleeve 522. A second O-ring seals theinterface between coil assembly 148 and a washer 542 attached to sleeve522.

Spool 144 defines first flange 164 which controls fluid flow betweenannular inlet chamber 534 and annular outlet chamber 536 and secondflange 166 that controls fluid flow between annular inlet chamber 534and annular outlet chamber 538. Flanges 164 and 166 thus control fluidflow between upper working chamber 244 and lower working chamber 246.

Coil assembly 148 is disposed within sleeve 522 to control the axialmovement of spool 144. The wiring connections for coil assembly 148extend to circuit board 524 and then through internal bore 512 of pistonrod 508. Circuit board 524 is disposed in internal bore 302 immediatelyabove the plurality of digital valve assemblies 510. An O-ring seals theinterface between circuit board 524 and piston rod 508. While circuitboard 524 is illustrated as being in internal bore 512, it is within thescope of the present disclosure to locate circuit board 524 external toshock absorber 220.

When there is no power provided to coil assemblies 148, the dampingcharacteristics will be defined by the flow area of digital valveassemblies 510 in the first position and piston assembly 232. Themovement of each spool 144 is controlled by supplying power to each coilassembly 148 to move digital valve assemblies 510 to the secondposition. Digital valve assemblies 510 can be kept in the secondposition by continuing to supply power to each coil assembly 148 or byproviding means for retaining digital valve assemblies 510 in the secondposition and discontinuing the supply of power to coil assemblies 148.The means for retaining digital valve assemblies 510 in the secondposition can include mechanical means, magnetic means or other meansknown in the art. Once in the second position, movement to the firstposition can be accomplished by terminating power to each coil assembly148 or by reversing the current or reversing the polarity of the powersupplied to each coil assembly 148 to overcome the retaining means. Theamount of flow through each digital valve assembly 510 has discretesettings for flow control in both the first position and the secondposition. While the present disclosure is described using multipledigital valve assemblies 510, it is within the scope of the disclosureto use one digital valve assembly 510. When multiple digital valveassemblies 510 are used, the total flow area through the plurality ofdigital valve assemblies 510 can be set at a specific number of totalflow areas depending on the position of each individual digital valveassemblies 510. The specific number of total flow areas can be definedas being 2^(n) flow areas where n is the number of digital valveassemblies 510. For example, if four digital valve assemblies 510, thenumber of total flow areas available would be 2⁴ or sixteen flow areas.

The force vs. velocity curve for shock absorber 20 illustrated in FIG. 7is applicable to shock absorber 220 in cooperation with the plurality ofdigital valve assemblies 510. The curves A, B, C and D illustrated inFIG. 7 are achieved using digital valve assemblies 510.

Referring now to FIGS. 15 and 16, a shock absorber 620 in accordancewith another embodiment of the present disclosure is illustrated. Shockabsorber 620 can replace shock absorber 20 or 220. Shock absorber 620comprises a pressure tube 630, piston assembly 32, piston rod 34, areserve tube 636, a base valve assembly 638, an intermediate tube 640and a plurality of digital valve assemblies 642. While shock absorber620 is illustrated having a plurality of digital valve assemblies 642,it is within the scope of the present disclosure to utilize a singledigital valve assembly 642.

Pressure tube 630 defines a working chamber 644. Piston assembly 32 isslidably disposed within pressure tube 630 and divides working chamber644 into an upper working chamber 646 and a lower working chamber 648. Aseal is disposed between piston assembly 32 and pressure tube 630 topermit sliding movement of piston assembly 32 with respect to pressuretube 630 without generating undue frictional forces as well as sealingupper working chamber 646 from lower working chamber 648. Piston rod 34is attached to piston assembly 32 and extends through upper workingchamber 646 and through an upper rod guide assembly 650 which closes theupper end of pressure tube 630. A sealing system seals the interfacebetween upper rod guide assembly 650, reserve tube 636 and piston rod34. The end of piston rod 34 opposite to piston assembly 32 is adaptedto be secured to the sprung mass of vehicle 10. Because piston rod 34extends only through upper working chamber 646 and not lower workingchamber 648, extension and compression movements of piston assembly 32with respect to pressure tube 630 causes a difference in the amount offluid displaced in upper working chamber 646 and the amount of fluiddisplaced in lower working chamber 648. The difference in the amount offluid displaced is known as the “rod volume” and during extensionmovements it flows through base valve assembly 638. During a compressionmovement of piston assembly 32 with respect to pressure tube 630,valving within piston assembly 32 allow fluid flow from lower workingchamber 648 to upper working chamber 646 and the “rod volume” of fluidflow flows through digital valve assemblies 642 and/or fluid flow willflow through base valve assembly 638 as described below.

Reserve tube 636 surrounds pressure tube 630 to define a fluid reservoirchamber 652 located between tubes 640 and 636. The bottom end of reservetube 636 is closed by a base cup 654 which, with the lower portion ofshock absorber 620, is adapted to be connected to the unsprung mass ofvehicle 10. The upper end of reserve tube 636 is attached tointermediate tube 640 but it could extend up to upper rod guide assembly650. Base valve assembly 638 is disposed between lower working chamber648 and reservoir chamber 652 to control the flow of fluid fromreservoir chamber 652 to lower working chamber 648. When shock absorber620 extends in length, an additional volume of fluid is needed in lowerworking chamber 648 due to the “rod volume” concept. Thus, fluid willflow from reservoir chamber 652 to lower working chamber 648 throughbase valve assembly 638 as detailed below. When shock absorber 620compresses in length, an excess of fluid must be removed from lowerworking chamber 648 due to the “rod volume” concept. Thus, fluid willflow from lower working chamber 648 to reservoir chamber 652 throughdigital valve assemblies 642 and/or through base valve assembly 638 asdetailed below.

Piston assembly 32 is described above for shock absorber 20 and thedescription of that embodiment applies here also.

Base valve assembly 638 is the same as base valve assembly 38 describedabove except that valve body 92 in base valve assembly 38 is replaced byvalve body 692 for base valve assembly 638. Valve body 692 is the sameas valve body 92 in relation to compression valve assembly 94 andrebound valve assembly 96. Valve body 692 is different from valve body92 in that valve body 692 defines a plurality of cylinder end ports 694each of which accepts a respective digital valve assembly 642 asdescribed below.

Intermediate tube 640 engages upper rod guide assembly 650 on an upperend and it engages valve body 692 at its opposite end. An intermediatechamber 696 is defined between intermediate tube 640 and pressure tube630. A passage 698 is formed in upper rod guide assembly 650 for fluidlyconnecting upper working chamber 646 and intermediate chamber 696.

Referring to FIGS. 16 and 17, the operation of shock absorber 620 willbe described when digital valve assemblies 642 contribute to the dampingcharacteristics for shock absorber 620. As discussed above, when nopower is provided to digital valve assemblies 642, the dampingcharacteristics are provided by piston assembly 32 during an extensionstroke and base valve assembly 638 during a compression stroke. During arebound or extension stroke, compression valve assembly 62 closes theplurality of compression passages 70 and fluid pressure within upperworking chamber 646 increases. Fluid is forced from upper workingchamber 646, through passage 698, into intermediate chamber 696 to reachdigital valve assemblies 642.

During a compression stroke, compression valve assembly 62 will open toallow fluid flow from lower working chamber 648 to upper working chamber646. Due to the “rod volume” concept, fluid in upper working chamber 646will flow from upper working chamber 646, through passage 698, intointermediate chamber 696 to reach digital valve assemblies 642.

The plurality of digital valve assemblies 642 are the same and only onedigital valve assembly 642 will be described. It is to be understoodthat the description below applies to all of digital valve assemblies642. Digital valve assembly 642 is a two position valve assembly whichhas a different flow area in each of the two positions. Digital valveassembly 642 comprises a sleeve 742, spool 144, a spring 146 and coilassembly 148. Sleeve 742 defines a valve inlet 750 which is incommunication with intermediate chamber 696 and a valve outlet 752 whichis in fluid communication with reservoir chamber 652.

Sleeve 742 is disposed within cylinder end port 694 of valve body 692.Sleeve 742 defines an annular inlet chamber 754 which is incommunication with valve inlet 750 and a pair of annular outlet chambers756 and 758 which are in communication with valve outlet 752.

Spool 144 is slidingly received within sleeve 742 and axially travelswithin sleeve 742 between coil assembly 148 and a stop puck 760 disposedwithin sleeve 742. Spring 146 biases spool 144 away from coil assembly148 and towards stop puck 760. A shim 762 is disposed between coilassembly 148 and sleeve 742 to control the amount of axial motion forspool 144. A first O-ring seals the interface between stop puck 760,sleeve 742 and a first retainer 764 attached to sleeve 742. A secondO-ring seals the interface between coil assembly 148, sleeve 742 and asecond retainer 766 attached to sleeve 742.

Spool 144 defines first flange 164 which controls fluid flow betweenannular inlet chamber 754 and annular outlet chamber 756 and secondflange 166 that controls fluid flow between annular inlet chamber 754and annular outlet chamber 758. Flanges 164 and 166 thus control fluidflow from intermediate chamber 696 to reservoir chamber 652.

Coil assembly 148 is disposed within sleeve 742 to control the axialmovement of spool 144. The wiring connections for coil assembly 148 canextend through valve body 692, through sleeve 742, through base cup 654and/or through reserve tube 636. When there is no power provided to coilassembly 148, the damping characteristics will be defined by the flowarea of digital valve assembly 642 in its first position, pistonassembly 32 and base valve assembly 638. The movement of spool 144 iscontrolled by supplying power to coil assembly 148 to move digital valveassembly 642 to its second position. Digital valve assembly 642 can bekept in its second position by continuing to supply power to coilassembly 148 or by providing means for retaining digital valve assembly642 in its second position and discontinuing the supply of power to coilassembly 148. The means for retaining digital valve assembly 642 in itssecond position can include mechanical means, magnetic means or othermeans known in the art. Once in its second position, movement to thefirst position can be accomplished by terminating power to coil assembly148 or by reversing the current or reversing the polarity of the powersupplied to coil assembly 148 to overcome the retaining means. Theamount of flow through digital valve assembly 642 has discrete settingsfor flow control in both the first position and the second position.While the present disclosure is described using multiple digital valveassemblies 642, it is within the scope of the disclosure to use onedigital valve assembly 642. When multiple digital valve assemblies 642are used, the total flow area through the plurality of digital valveassemblies 642 can be set at a specific number of total flow areasdepending on the position of each individual digital valve assemblies642. The specific number of total flow areas can be defined as being2^(n) flow areas where n is the number of digital valve assemblies 642.For example, if four digital valve assemblies 642, the number of totalflow areas available would be 2⁴ or sixteen flow areas.

The force vs. velocity curve for shock absorber 20 illustrated in FIG. 7is applicable to shock absorber 620 in cooperation with the plurality ofdigital valve assemblies 642. The curves A, B, C and D illustrated inFIG. 7 are achieved using digital valve assemblies 642.

Referring now to FIGS. 18 and 19, a base valve assembly 838 inaccordance with another embodiment of the present disclosure isillustrated. Base valve assembly 838 is a replacement for base valveassembly 638. Base valve assembly 838 is the same as base valve assembly638 except for valve body 692. Valve body 692 in base valve assembly 638has been replaced with valve body 844 in base valve assembly 838. Valvebody 844 defines a plurality of cylinder end ports 846 each of whichaccepts a respective digital valve assembly 642. The operation andfunction of base valve assembly 838 is the same as that described abovefor base valve assembly 638.

Referring now to FIGS. 20 and 21, a base valve assembly 938 inaccordance with another embodiment of the present disclosure isillustrated. Base valve assembly 938 is a replacement for base valveassembly 638. Base valve assembly 938 is the same as base valve assembly638 except for valve body 692 and digital valve assembly 642. Valve body692 in base valve assembly 638 has been replaced with valve body 944 inbase valve assembly 938 and digital valve assembly 642 has been replacedwith a digital valve assembly 948. Valve body 944 defines a plurality ofcylinder end ports 946 each of which accepts a respective digital valveassembly 948. Digital valve assembly 948 is the same as digital valveassembly 642 except that sleeve 742 is replaced by sleeve 950. Sleeve950 is the same as sleeve 742 except that valve outlet 752 of sleeve 742is replaced by valve outlet 952 of sleeve 950. Valve outlet 752 ofsleeve 742 is open along the entire axial length of sleeve 742. Outlet952 of sleeve 950 is open only at the bottom surface of sleeve 950.

Digital valve assembly 948 is disposed within intermediate chamber 696as illustrated in FIG. 20. Intermediate tube 640 is enlarged as shown at960 to accommodate digital valve assembly 948. The operation andfunction of base valve assembly 938 is the same as that described abovefor base valve assembly 638.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention. Individual elements or features ofa particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the invention, and all such modificationsare intended to be included within the scope of the invention.

What is claimed is:
 1. A shock absorber comprising: a pressure tube forming a working chamber; a piston assembly slidably disposed within said pressure tube, said piston assembly dividing said working chamber into an upper working chamber and a lower working chamber, said piston assembly including a piston body defining a first fluid passage extending through said piston body and a first valve assembly controlling fluid flow through said first fluid passage; a second fluid passage separate from said first fluid passage, said second fluid passage extending from one of said upper and lower working chambers to a fluid chamber defined at least in part by said pressure tube; a plurality of digital valve assemblies configured to exclusively control all fluid flow through said second fluid passage and thus all fluid flow between said one of said upper and lower working chambers to said fluid chamber; wherein fluid flow through said first valve assembly generates a high damping load for said shock absorber; fluid flow through said first valve assembly and said digital valve assemblies cooperatively generates a low damping load, lower than said high damping load, for said shock absorber; and each of said plurality of digital valve assemblies includes a first member, a second member disposed within said first member to move in an axial direction within said first member, and a third member configured to move said second member in the axial direction; said second member and said first member of each one of said digital valve assemblies cooperating to exclusively control said fluid flow through said second fluid passage in the axial direction; each of the digital valve assemblies includes a single inlet, and a first outlet; and fluid flow from said single inlet to said first outlet is in a first direction substantially parallel to the axial direction.
 2. A shock absorber comprising: a pressure tube forming a working chamber; a piston assembly slidably disposed within said pressure tube, said piston assembly dividing said working chamber into an upper working chamber and a lower working chamber, said piston assembly including a piston body defining a first fluid passage extending through said piston body and a first valve assembly controlling fluid flow through said first fluid passage; a second fluid passage separate from said first fluid passage, said second fluid passage extending from one of said upper and lower working chambers to a fluid chamber defined at least in part by said pressure tube; at least one digital valve assembly for exclusively controlling all fluid flow through said second fluid passage, and thus all fluid flow flowing between said one of said upper and lower working chambers and said fluid chamber; wherein fluid flow through said first valve assembly generates a high damping load for said shock absorber; fluid flow through said first valve assembly and said at least one digital valve assembly generates a low damping load, lower than said high damping load, for said shock absorber; and said digital valve assembly includes a first member, a second member disposed within said first member to move in an axial direction within said first member and a third member configured to move said second member in the axial direction; said second member and said first member cooperating to control fluid flow in the axial direction through said digital valve assembly; said digital valve assembly including an annular inlet chamber and an outlet chamber; and fluid flow from said annular inlet chamber to said outlet chamber of said digital valve assembly is turned 90 degrees from a radial flow to a flow having a direction substantially parallel to the axial direction, by said digital valve assembly.
 3. A shock absorber comprising: a pressure tube forming a working chamber; a piston assembly slidably disposed within said pressure tube, said piston assembly dividing said working chamber into an upper working chamber and a lower working chamber, said piston assembly including a piston body defining a first fluid passage extending through said piston body and a first valve assembly controlling fluid flow through said first fluid passage; a second fluid passage separate from said first fluid passage, said second fluid passage extending from one of said upper and lower working chambers to a fluid chamber defined in part by said pressure tube; a plurality of digital valve assemblies for exclusively controlling all fluid flow through said second fluid passage, and thus all fluid flow from said one of said upper and lower working chambers to said fluid chamber; wherein fluid flow through said first valve assembly generates a high damping load for said shock absorber; fluid flow through said first valve assembly and said digital valve assemblies generates a low damping load, lower than said high damping load, for said shock absorber; each of said plurality of digital valve assemblies includes a first member, a second member disposed within said first member to move in an axial direction within said first member, and a third member configured to move said second member in the axial direction; said second member and said first member cooperating to control fluid flow in the axial direction through each said digital valve assembly; each of said digital valve assemblies including an annular chamber surrounding the second member; and fluid flow through each said digital valve assembly is in a direction substantially parallel to the axial direction. 